The present invention relates to a sensor network system, a sensor node, a sensor information collector, a method of observing an event, and a program thereof, and more particularly to a sensor network system having a sensor information collection function with a high precision (high resolution) and a congestion suppression function, a sensor node, a sensor information collector, a method of observing an event, and a program thereof.
As a means for collecting information detected by a plurality of sensors installed in a room, a building, etc. there exists a sensor network. The sensor network includes a sensor node that detects and transmits the event.
And, so as to enhance a precision (resolution) of the information detected by the sensor, there exist the apparatus for shortening a period at which the sensor node transmits information, thereby to enhance a temporal resolution (see, for example, patent document 1, identified below) and the method of enhancing a spatial resolution by increasing a spatial density of the sensor node that transmits information.
Further, so as to avoid the problem (response implosion problem) that all of the sensor nodes observing the identical event result in transmitting a large quantity of information all at once, there exists the method of transmitting information by each sensor node after a delay time that differs sensor node by sensor node, thereby to allow the congestion to be avoided (see, for example, patent document 2, identified below), and the method of selecting the sensor node at random that transmits information (see, for example, non-patent document 1, identified below).
Additionally, explanation of a Markov random field is described in non-patent document 2, identified below.
[Patent document 1] JP-P1982-202161A (FIG. 1)
[Patent document 2] JP-P2001-45020A (Paragraphs 0022 to 0041, and FIG. 1)
[Non-Patent document 1] C. Shen and two others, “Sensor Information Networking Architecture and Applications”, IEEE Personal Communications, U.S., August, 2001, p. 52-59
[Non-Patent document 2] Kazuyuki TANAKA “Theoretical Study of Hyperparameter Estimation by Maximization of Marginal Likelihood in Image Restoration by Means of Cluster Variation Method”, IEICE Transactions (A), the Institute of Electronics, Information and Communication Engineers. Vol. J83-A, No. 10, pp. 1148-1160. October, 2000.
However, like the case of the apparatus described in the patent document 1, shortening the period at which the sensor node transmits information in some cases, or increasing the spatial arrangement density of the sensor node in order to enhance the spatial resolution of information that the sensor node transmits in some cases causes the response implosion problem that all of the sensor nodes having observed the identical event transmit a large quantity of data all at once. And, the communication network could get congested in some cases, and the information processing ability in the reception side that receives data could be exceeded in some cases.
The reason is that, in the prior art, it is impossible to enhance the precision (resolution) of information, which the sensor node transmits, without increasing the traffic quantity.
Further, in the method described in the patent document 2, or the method described in the non-patent document 1, for example, a random delay time in transmission is inserted, or the sensor node transmitting data is adopted or rejected at random as a control of transmitting sensor data in order to avoid all of the sensor nodes observing the identical event from transmit a large quantity of data all at once. For this, the precision (resolution) of information could decline because the information communication quantity a unit time decreases in some cases, and the number of the sensor node transmitting information decreases in some cases.
The reason is that the conventional sensor network system takes no consideration into reducing the traffic without lowering the precision (the temporal resolution and the spatial resolution) of information that the sensor transmits.
Thereupon, the present invention has an object of providing a sensor network system that enables information of which the precision (temporal resolution and spatial resolution) is high to be collected and the congestion due to information transmitted by the sensor node to be suppressed, a sensor node, a sensor information collector, a method of observing an event, and a program thereof.